In electrical-discharge machining of this type, which is commonly called "wire-cut EDM" or "travelling-wire EDM", the wire electrode held under tension is displaced to travel through a machining zone to be cut in the workpiece and flushed with a machining liquid which is usually a distilled water or liquid dielectric and a series of electric pulses are applied across the machining gap between the wire electrode and the workpiece to effect time-spaced electrical discharges between them to remove material from the workpiece.
Typically, the wire electrode is fed from a supply reel and passes through the machining zone between a pair of support and guide members which act to stretch the travelling wire electrode thereacross and fed to a take-up reel by a drive motor, the tension of the wire electrode between the guide members being controlled by a suitable brake mechanism arranged at a location or locations in the travelling path thereof.
The transverse displacement of the workpiece relative to the travelling-wire electrode to follow the material removal is usually effected automatically by a control system under programmed instructions which define a predetermined cutting path or pattern.
In order to achieve a satisfactory machining accuracy, it is necessary to use a wire electrode as thin as 0.05 to 0.5 mm diameter. This requirement, however, has heretofore imposed restrictions in the machining performance attainable. Such a thin wire, given a desired tension, tends to be broken even with incidental occurrence of arcing or short-circuiting with the workpiece. Thus, the machining efficiency or removal rate achievable has been limited to an unsatisfactory level since the wire breakage is unavoidable when an enhancement of machining or an increase in the rate of relative displacement is attempted.